In conventional pyrolysis, bulky carbonaceous feedstock is partially combusted to raise the temperature of feedstock (partial oxidation method) and consequently to produce gas and solid char/cokes. The flue gas is combusted in the second stage reactor, and the heat generated is put back into the first stage to further increase the temperature for pyrolysis. The remnant solid disposed in the solid disposal dump.
More recently, it has been reported that the combustion of flue gas with O2 gas, is used to gasify solid char/coke into syngas (DE 19536383-A1). Flue gas is a mixture of gases, some of them quite toxic, need to be combusted in the second stage reactor, before it can be let out into the atmosphere.